1. Field of Invention
The present invention relates to the field of digital video broadcasting, and more particularly to a channel estimation method and system based on a time-domain training sequence.
2. Description of Related Arts
The broadcast channel has the characteristics as follows: 1) the delay is long, and is up to hundreds of symbol rate intervals; 2) in a single orthogonal frequency-division multiplexing (OFDM) block, the channel response does not change or changes slightly; and 3) various additive interferences exist extensively. Therefore, the researchers focus on how to estimate a channel accurately to decode data.
The existing channel estimation method mainly includes:
1. Che-Shen Yeh, et. al have proposed an estimation method based on a training sequence in the document “Che-Shen Yeh, Yinyi Lin, and Yiyan Wu, OFDM System Channel Estimation Using Time-Domain Training Sequence for Mobile Reception of Digital Terrestrial Broadcasting, IEEE TRANSACTIONS ON BROADCASTING, VOL. 46, NO. 3, SEPTEMBER 2000”.
2. Yan-Chang Chen, et. al have in the document “Yan-Chang Chen, Wen-Jeng Lin, Jung-Shan Lin, Channel Estimation Technique with Assistance of PN-Coded Training Sequences for Wireless OFDM Communications, IWCMC'07” have analyzed the performance of channel estimation by using the least-square (LS), simplified LS (SLS), the hybrid LS (HLS), and maximum likelihood (ML).
3. Lei Zhou, et. al have proposed a channel estimation method based on a known delay in the PRC Patent Document with the Publication No. CN 1346187A, in which a conjugate gradient algorithm is used to estimate a channel response of a code division multiple access (CDMA) system at a known channel location to eliminate the data interferences.
4. Jin H. Kim, et. al have proposed a series of channel estimation methods for the Advanced Television Systems Committee (ATSC) in the US Patent Document with the Application No. 729722 and the theme “Efficient conjugate gradient based channel estimator”, in which the information of the decoding feedback is particularly used as a training sequence and the minimum mean square error (MMSE) criterion is used to acquire the channel estimation. To simplify the implementation, the FFT is further used to perform the conjugate gradient update.
5. Mark, Fimoff, et. al have proposed a channel estimation method combining correlation and least-square in the U.S. Pat. No. 7,035,353 and U.S. Pat. No. 7,203,257, and this method requires to prestore a training matrix and a noise square error.
6. Emre Telatar, et. al have pointed out in the document “Aslan Tchamkerten and I. Emre Telatar, On the Use of Training Sequences for Channel Estimation, IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 52, NO. 3, MARCH 2006” that the method that combines the channel estimation and reception can acquire the optimal performance. However, in practical applications, the two are actually separated, and the channel estimation greatly affects the system performance.
In the China Terrestrial Television Broadcasting (CTTB) system, as the used training sequence has the relatively weak correlative characteristic, when the method proposed by Che-Shen Yeh, et. al is used, the system performance is deteriorated in the case of direct correlation. The method provided by Yan-Chang Chen, et. al is too complicated and highly inapplicable. For the rest estimation methods, as in a mode 1 and a mode 3 of the CTTB, the phase of the training sequence might be changing, so the method proposed by Mark, Fimoff, et, al, in which the matrix and noise square error are stored to implement the channel estimation of LS, requires the use of a very large storage unit and is thus inapplicable. However, when the MMSE based estimation method proposed by Jin H. Kim, et. al is used, the on-line computational load is heavy and the delay in acquiring the training sequence through the decoding feedback is also unacceptable.